In a conventional vehicle-mounted CD/MD receiver comprising a display device and a touch panel which function as a man-machine interface, an operating screen on which dedicated operating key figures assigned to respective functions are arranged is displayed to allow operation corresponding to each operating key by pressing the operating key though the touch panel. In some cases, an inferior adjustment mode operating screen is displayed by pressing a menu key or the like, and operation is performed by, e.g., pressing an operating key within the operating screen.
FIG. 2 illustrates the outer appearance of such a conventional CD/MD receiver. This device comprises a display 1 for displaying a screen and a touch panel 2 for pressing the displayed screen on the display 1, thereby inputting coordinates corresponding to the press position. The device displays an operating screen 21 on which operating keys 20 and 23 to 30 corresponding to operations for executing respective functions are arranged. The device is configured to acquire operation content specified by a press on the operating screen 21 from the display positions of the operating keys, operations corresponding to the operating keys, and input coordinates obtained from the touch panel 2.
As a vehicle information display device such as car navigation equipment having a man-machine interface like the CD/MD receiver, a device which switches the combination of the colors of drawing elements in an operating screen depending on whether a vehicle is at a stop or traveling or whether the device is used in the daytime or at night is proposed in, e.g., Japanese Patent Laid-Open No. 7-191612. According to the document, since this device displays input keys inoperable and ones operable at the time of traveling such that they can be easily discriminated from each other, it is possible to safely operate an input key even at the time of traveling and reduce unnecessary input operation.
However, since the conventional CD/MD receiver requires each operating key to be operated while carefully looking at a displayed screen, it is difficult to operate the operating key while a vehicle is traveling. For this reason, operation of an operating key needs to be performed after the vehicle is stopped. That is, operation at the time of traveling has several problems. More specifically, it may be impossible to easily recognize which one of displayed operating keys is to be pressed. An operating key adjacent to one desired to be pressed may be mistakenly pressed. It may be dangerous to perform fine operation at the time of driving the vehicle because fine operation requires a careful look at the screen. One with poor eyesight may need to move his or her face closer to the screen. It may not be easy for some people to operate the operating keys because the arrangement and sizes thereof are always the same. One may get tired of looking at the display because there is no change in it. All the operating keys may be exactly the same to the touch with fingers in operating them, and thus it may be necessary to visually confirm operation.
According to the vehicle information display device, discrimination of operable input keys is facilitated. However, the vehicle information display device has the same problems as described above. More specifically, it may be difficult to immediately recognize which input key is to be operated. It may be not easy for some people to operate input keys because the arrangement and sizes thereof are always the same.
The present invention has been made in consideration of the prior art drawbacks, and has as its object to provide a man-machine interface technique for allowing easy and reliable operation.